As discussed in my previous application, identified above, the sole plates of screeds on asphalt paving machines must be preheated to about 175.degree. F. to 200.degree. F. before paving commences to keep the hot asphalt from congealing on the sole face of the screeds. In the past, the preheating has been accomplished by oil or propane burners mounted on the moldboard and directly heating the top surface of the screeds. When using such burners, particular care must be taken to avoid overheating since this can result in permanent warping of the screed.
U.S. Pat. No. 4,818,140 discloses a screed extension which is slide-mounted on the moldboard of an asphalt paver of the floating screed type. The screed extension is divided into inner and outer screed sections which are hinged together so that the outer screed section can be swung upwardly relative to the inner screed section to engage and shape a sloping berm. Prior to the heating system disclosed in my previous application, screed extensions have not been independently heated because the preheating system normally used for the main screed was not considered to be adaptable for screed extensions.
My prior invention provided an improved preheating system applicable to both primary and extension screeds which eliminated the use of oil or propane burners by utilizing the heat created by dropping the pressure of high pressure oil at a flow restrictor. A reservoir was mounted in direct contact with the top surface of the screed, and oil from the reservoir was pressurized by a pump and circulated through a flow restrictor to create a large pressure drop. This pressure drop can be adjusted to result in an output oil temperature of about 275.degree. F. which normally is sufficient to establish the desired screed temperature of about 200.degree. F.